The enzyme rhodanese (EC 2.8.1.1, thiosulfate sulfurtransferase) offers an opportunity to study and understand several features of protein structure and fluctuations of this structure that are important in enzyme catalysis. This study of rhodanese is of interest for a number of reasons: the kinetics of the enzyme are well understood; the x-ray structure is known to a resolution of 2.5 A for one enzyme form; it displays conformational changes during catalysis; it is folded into distinct domains with the active site in the interdomain region; and it displays a number of non-artifactual discrepancies between the x-ray and solution studies, which reflect the flexibility of this protein. The proposed research is designed to establish and pursue correlations between the possibly flexible conformational states of rhodanese and the catalytic events in which it participates. Steady-state fluorescence and fluorescence lifetime techniques will be used as the major methodology and the results will be correlated with data from x-ray analysis, other physico-chemical techniques and kinetic studies. An underlying objective of this research is to develop a set of diagnostics, approaches and techniques for the recognition and study of the role of protein flexibility in other functional systems.